Washington and British Columbia. 643 



A peculiar form of algae grows in this larger lake near 

 the surface. A film of sodium sulphate is also present 

 near the surface, which is absent in the other lake. Other 

 briny lakes in this country were visited, and it was found 

 that in most of these sodium sulphate predominated and 

 also that extensive growth of algae was noticeable. There 

 is one such sodium sulphate lake within a short distance, 

 just over the hill from this large epsomite lake. In some 

 of these lakes faint traces of the spotted appearance could 

 be detected in the arrangement of the mud beneath the 

 surface of the water. 



Discussion in regard to structure of the mineral deposit 

 and to origin 2 and source of the material will necessarily 

 have to be confined to the smaller lake in Washington, 

 where the writer spent more time studying conditions. 

 In this regard, let us go back to the description of this 

 lake, and its surrounding territory. In addition to what 

 was said, the pyrite and pyrrhotite deposits were oxidized 

 to a depth of several feet from the surface to a mixture 

 of iron oxides, quartz, clay, and tiny crystals of gypsum. 

 Leading from these deposits to the lake were drainage 

 ways, on the surface of which, in places, showed whitish 

 alkali streaks. 



These facts suggest the possibility that the sulphates 

 and sulphuric acid, known to form from the oxidation of 

 pyrite and pyrrhotite through the action of meteoric 

 water and air, acted upon the dolomite and other magne- 

 sian rocks, forming magnesium sulphate, which is soluble, 

 and calcium sulphate, which is much less soluble. The 

 result was that the magnesium sulphate was carried to 

 the lake in solution. What little calcium sulphate came 

 with it was precipitated first, being less soluble, as a thin 

 layer of gypsum over the sediment already deposited on 

 the bottom of the lake. 



This explains the formation of the horizontal layer of 

 epsomite above the gypsum. The layer of mud on top 

 of the epsomite layer is accounted for by the washing 

 of sediment into the lake. The fresher water allowed 

 some organic life to thrive, but with the increasing salin- 

 ity of the lake, due to increased aridity, the organisms 



2 F. M. Handy : An investigation of the mineral deposits of northern 

 Okanogan County, State College of Washington, Bulletin No. 100, Pullman, 

 Wash. (Suggestion is made regarding the origin of the salts in the smaller 

 lake, which coincides with the theory in the present paper.) 



